Dry fiber distribution

ABSTRACT

Fibers are suspended in a rising stream of air which is deflected into a distribution chamber having a bottom formed by a belt-like, gas-permeable screen advanced over a suction box, whereby a dry fiber web is produced on said screen. At the deflection of the fiber-carrying air stream a second stream of air is added to control the inflow of suspended fibers into the distribution chamber and to cause the fibers to follow a trajectory through said chamber. The pattern of fiber deposition on the moving screen is further controlled by admitting additional air from above through an adjustable opening in the enclosure of the distribution chamber.

[ Feb. 19, 1974 3,635,627 1/1972Palmer................................425/141 2,219,346

[ DRY FIBER DISTRIBUTION 10/1940 Thomas et al. 425/83 X Inventor: JonasAnders Giite Helgesson, Taby,

Sweden Primary ExaminerRobert L. Spicer, Jr.

Attorney, Agent, or Firm-Fred C. Philpitt [73] Assignee: IngenjorsfirmaB-projekt Aktiebolag, Enebyberg, Sweden Sept. 23, 1971 [57] ABSTRACTFibers are suspended in a rising stream of air which is 22 Filed:

[21] Appl' deflected into a distribution chamber having a bottom formedby a belt-like, gas-permeable screen advanced over a suction box,whereby a dry fi her web is pro- [30] Foreign Application Priority DataOct. 14, 1970 Sweden.............................

3 2 70 duced on said screen. At the deflection of the fibercarrying airstream a second st ream of air is added to .l an ma w hO O mf no .I SSrr Ce bb an d [52] US. 425/83, 425/141, 264/91, r l he inflow ofsuspends 264/109 bution chamber and to cause the F1 jectory through saidchamber. Th

position on the moving screen is admitting additional air able openingin the enclosure 0 chamber.

09 00 l 5 7 04 2 B4. ,6 02 0... /l 4 c i 9% d m C mm mfi m 4 e m H Tm aMr R a "e "S l m cm e .mF HM N 55 5 UNITED STATES PATENTS 3,671,2106/1972 Richardson....................... 425/83 X 13 Claims, 2 DrawingFigures 1 DRY FIBER DISTRIBUTION This invention relates to themanufacture of more or less felted fiber products from natural orartificial fibers, such as wood fibers, textile fibers, glass andmineral wool fibers, asbestos fibers and the like, and more particularlythe invention is concerned with the production of webs of such fibers ona gas-permeable screen, commonly made of wire fabric, while applying aso-called dry process in which flowing gas is used as a medium to sort,transport and distribute the fibers. The dry process referred tocomprises two main steps, viz. first suspending the fibers in avertically rising gas stream and subsequently distributing the suspendedfibers over a gas-permeable screen that is advanced at the bottom of aso-called distribution chamber and has its underside exposed to anegative pressure, the rising fiber-carrying gas stream being admittedinto the distribution chamber in a substantially horizontal direction.

As compared to the wet processes hitherto most commonly applied tomaking paper or similar web-type fiber products, the use ofa gas insteadof water or other liquid as a suspension medium for the fibers to bedistributed over a wire offers many advantages. This is true not onlyfromm the viewpoint of safe-guarding the environment but in particularin those cases where the fibers themselves contain liqud-soluble matterswhich would contaminate the water or where the fibrous material for onereason or the other isintermixed with soluble impurities that aredifficult to remove. In addition, the wet process commonly requirespreparatory drying of the produced web, before the latter can besubjected to the pressing, with or without heating, which is usuallyrequired for finishing the product. Also, the wet process isobjectionable, when it is desirable e.g. to impregnate the fibers or tocover them with adhesive before the web is being formed, because in sucha case large quantities of impregnating agent or adhesive will be lostin the carrier liquid.

Although the dry process for the production of webs of more or lessfelted fibers as referred to hereinbefore has been known for more thanhalf a century, it has only rarely, if at all, been applied in practice.Instead great efforts have been made to develop rather complicatedmechanical means for strewing dry fibers over a moving wire withoutletting them become sorted and literally transported by a gas stream. Sofar the practical results of these efforts have been unsatisfactory forseveral reaons. Among other things, it has been found verydifficult'with the strewing method to meet the requirements as touniformity in thickness of the produced web, and it is almost impossibleto obtain that controlled distribution of finerand coarser fibers in thethickness direction of the web, which is frequently important in orderto give the product the desired properties.

Alreadywhen the first attempts were once made to substitute a gaseousmedium, such as air, for water as a fiber carrier in the distribution ofloose fibers over a movable wire, a vertical shaft or duct was used, inwhich a rising gas stream was-created and caused to carry along fibersthat in one way or the other were spread or thrown into the gas stream.Almost from the beginning, it was also suggested that the risingfibercarrying gas stream should be deflected in a substantiallyhorizontal direction and then be admitted into a distribution chamber,where the fibers were permitted to fall down towards an endless wire orscreen that was advanced over a suction box at the bottom of thedistribution chamber. Unfortunately, great difficulties came up whenthis basic idea should be put into practice. Firstly, it was found thatthe fibers were swept away rather irregularly by the gas stream and hada great tendency to get stuck and deposit in the duct connecting thevertical shaft to the distribution chamber. Secondly, it was difficultto obtain a uniform distribution of the fibers on the wire or screen,before all in the transverse direction thereof, and also to adjust thethickness of the fiber web formed on the wire in a sufficiently reliablemanner.

Accordingly, it is the object of this invention to offer a simple andpractical solution of these specific problems. With these and otherobjects in view the invention consists, primarily, in a method ofdistributing fibers suspended in a vertically rising gas stream over agas-permeable screen being advanced at the bottom of a distributionchamber and having its underside exposed to a negative pressure, therising fiber-carrying gas stream being admitted into the distributionchamher in a substantially horizontal direction. The invention alsoconsists in an improved apparatus for producing fiber webs in a dryprocess by carrying out the beforementioned method. Basically, theinvention overcomes the inconveniences referred to hereinbefore bysuggesting that additional gas streams should be used for controllingthe fiber-carrying gas stream as it enters the distribution chamber fromthe vertical shaft or duct, and also for controlling the patternaccording to which the fibers are distributed and deposited over and onthe wire or screen within said distribution chamher.

For a more complete elucidation of the invention an embodiment thereofwill be described in the following and with reference to theaccompanying drawing. In the drawing FIG. 1 shows a slightlydiagrammatic sectional elevation of an apparatus embodying the inventionand useful for distributing fibers suspended in a gas stream over amovable, endless wire or screen, while FIG. 2 is a fragmentary frontview of the apparatus as seen from the line IIII in FIG. 1.

The section in FIG. 1 is taken in the running direction of the wire, andit shold be understood that the wire can, of course, have any desiredwidth, whereas the width of the fiber distributing means forming part ofthe apparatus can be adapted either to the entire width of the wire orto the width of a selected part thereof, if it is desirable to form afiber web that is narrower than the wire itself. In practice, this meansthat the apparatus shown in FIG. 1 usually has a considerably largerextension perpendicularly to the plane of the drawing than in thisplane.

Referring to FIG. 1, an endless, flexible and gas permeable screen 1,suitably of close-meshed wire cloth, runs over conducting and supportingrollers 2, 3 and 4 and passes over an upwardly open suction box 5, theinterior of which is connected to a suction source, not shown, e.g. inthe form of a suction ventilator having a relatively large capacity, sothat a negative pressure can be maintained in the suction box under thewire 1. Suitable means, not shown, are provided for driving the wire ata preferably adjustable speed. Above the section of the wire that passesover the suction box there is arranged a distribution chamber,genhorizontal, movable bottom of a generally rectangular shape in thedistribution chamber. In FIG. 1 the wire 1 is supposed to move from theleft to the right as indicated by an arrow but, as it will appear fromthe following, it is also possible to reverse the moving directionthereof in order to achieve special productional results. The requiredseal between the wire 1 and the wall portions of the distributionchamber 6 extending across the wire is obtained by means of rollers 7which are movable towards and away from the wire and against which leansealing flaps 8 hinged to the outer sides of the respective distributionchamber walls. One of the rollers 7 will then come to roll in directengagement with the wire 1, as shown to the left in FIG. 1, whereas theother one will roll on top of the fiber web 9 formed on the wire, asshown to the right in FIG. 1.

The distribution chamber 6 has a vertical crosssection as seen in therunning direction of the wire, FIG. 1, that generally takes the form ofasector ofa circle, the one bounding radius of said sector beingrepresented by the section of the wire 1 extending over the suction box5, the other bounding radius being represented by a vertical wall member10 extending across the wire, and the bounding are being represented bya curved cap or hood 11. The latter forms the top and the right handwall of the distribution chamber 6 and has approximately at the middleof its are, a slot-shaped opening 12 extending in the entire width ofthe distribution chamber, i.e., perpendicularly to the plane of thedrawing. This elongate opening 12 is provided with an upper adjustabledamper plate 13 extending along the entire length thereof and also witha horizontal series of lower damper plates 14 mounted adjacent eachother in successive order and being individually adjustable in thedirection towards and away from the upper damper plate 13 for varying,section by section, the width and, hence, to a certain extent also ofthe configuration of the opening 12, as can be seen from FIG. 2. Byadjusting the damper plate 13, the general size of the opening 12 and toa certain extent also the angular position thereof in the hood 11 canobviously be varied. The opening 12 puts the interior of thedistribution chamber 6 in communication either with the external air asshown, or with a duct for closed delivery of gas, not shown.

The upper part or top of the hood 11 is extended towards the left beyondthe wall member 10 and is separated from the upper edge of the latter byan opening 15 that in the plane of the wall member 10 is rectangular andhas a length corresponding to the width of the distribution chamber 6across the running direction of the wire 1. The portion or extension 11of the hood ll projecting outside the wall member 10 forms an upper,substantially flat and horizontal top cover for a shaft or vertical duct16 of substantially rectangular horizontal cross section, said shafthaving also a length corresponding to the width of the distributionchamber 6. The uppermost portion of the wall member 10 is common to boththe shaft 16 and the distribution chamber 6, i.e., the wall member 10forms a partition between the shaft and the distribution chamber. Theshaft 16 and the distribution chamber 6 also have a common end walls 17which in the illustrated form of apparatus extend downwardly on each oneside of the wire 1 and, in fact, represent the supporting end walls ofthe entire apparatus. The vertical shaft 16 is, on the side facing awayfrom the distribution chamberr 6, bounded by a vertical wall member 18,the upper edge of which is spaced from the hood extension 11' by aslot-shaped opening 19 extending horizontally between the end walls 17.The size of this opening is variable by means of a vertically adjustabledamper plate 20. lf desired, this single damper plate may be replaced bya series of smaller damper plates resembling the damper plates 14previously described, and in such a case not only the size but also theconfiguration of the opening 19 may be varied, which sometimes can beadvantageous. It is also possible to make and attach the damper plate 20in such a manner that the configuration of the opening 19 can be variedby tilting the damper plate in the plane of the wall member 18.

The vertical shaft 16 has its lower end connected to a chamber 21, atthe bottom of which there is arranged a conveyor screw 22 for theremoval of any such fiber material that is not carried upwards by thegas stream passing through the chamber 21 and the shaft 16. The chamber21 has a gas inlet opening 23 through which the main flow of air or gasenters the apparatus and the size of which is variable by means of anadjustable damper device 24. Like the opening 19, referred to above, thegas inlet opening 23 can be connected to the external air, as shown, orboth openings can communicate with a closed gas delivery duct e.g. fromthe suction source, if a closed gas circuit is desired.

Outside the wall member 18 is a feed chute 25 into which more or lessmatted together fiber bundles are supplied at a suitable, preferablyadjustable rate such as by means of a belt conveyor indicated at 26. Atthe lower end of the feed chute 25 there is mounted a rotarydisintegrator 27 in the form of a roller having a plurality of radiallyprojecting pins thereon. This roller is rotated in the clockwisedirection at a rather high speed for disintegrating the fiber bundlesreceived in the chute 25 and for throwing out the separated, free fibersinto the lower part of the shaft 16 and into the chamber 21 from whichthe shaft proceeds upwards. Usually, a small amount of air also entersthe apparatus through the feed chute 25, but this can be avoided, ifdesired, by delivering the fiber bundles into the chute through an airlock arrangement well known in itself but not shown.

The fiber bundles received in the feed chute 25 are broken up by therotating disintegrator 27 and the free fibers are caught and carriedalong upwards by the gas stream passing through the chamber 21 andrising through the shaft 16. Such fiber material that, for one reason oranother, is not carried away by the rising gas stream, gathers at thebottom of the chamber 21 and is removed by means of the conveyor screw22 which, of course, can be replaced by any other suitable feedingoutdevice. The removed residue of the fiber material may, if desired, bereturned to the feeding-in conveyor 26. The feed chute 25 and thedisintegrator 27 have a length corresponding to the length of thechamber 21 and that of the horizontal cross-section of the shaft 16,whereby a good distribution of the fibers in the entire shaft isachieved. In the chamber 21 an important fiber sorting will take place,whereby heavy fibers as well as unresolved fiber bundles and at leastcertain heavy im purities become separated, because the rising gasstream is unable to carry them upwards through the shaft 16.

As a result of the fact that air is admitted into the upper end of theshaft 16 immediately below the hood extension 11 through the opening 19,the deflection of the fibre-carrying gas stream through the opening 15into the distribution chamber 6 is greatly improved. In addition, thefact that the wall member forms only a thin partition between thedistribution chamber and the shaft 16 assists in preventinguncontrolable fiberdeposits. The second gas stream admitted through theopening 19 causes the fiber-carrying vertical gas stream to follow apath resembling a trajectory when entering the interior of thedistribution chamber and continuing towards the wire 1. By adjusting thesize of the opening 19, the thickness of the fiber web 9 formed on thewire 1 can be controlled within rather wide limits. Itt should be noted,however, that also the amount of fiber material supplied to theapparatus per time unit, as well as the running speed of the wire arefactors involved in determining the average thickness of the fiber webformed. By varying the configuration of the opening 19, the thickness ofthe fiber web formed on the wire 1 may be controlled in the transversedirection of the latter to a certain degree. Such transversal thicknesscontrol is, however, accomplished with better accuracy by means of theadditional gas stream entering the upper part of the distributionchamber 6 through the opening 12. This will result from the fact thatthe lastmentioned gas stream, although having a main direction fromabove and downwards in the distribution chamber, will also have acertain component of movement in a direction which more or less crossesthe fibercarrying gas stream and thereby disturbs its trajectory.

By sensing the thickness of the fiber web 9 in a plurality of pointsspaced in the transverse direction of the wire 1 by means of sensingmeans indicated at 28, which is suitably done slightly before the fiberweb is leaving the distribution chamber 6, and by letting these sensingmeans 28 govern the operation of small actuators 29 adjusting thepositions of the lower damper plates 14, possible tendencies ofthickness variations in the fiber web can be inhibited, so that, from apractical point of view, a uniform thickness of the fiber web isachieved over the entire width of the wire 1. If, on the other hand, itis desirable to produce a fiber web having a thickness that varies inthe transverse direction of the wire 1, a similar control may be used,of course, in order to obtain a desired corrugation of the upper side ofthe fiber web. In fact, the possibility of varying andd correcting thethickness of the fiber web in the way described is very striking andsurprising.

The gas-suspended fibers entering the distribution chamber 6 through theopening will follow a trajectory starting in a substantially horizontaldirection. As known per se, this will result in a certain and frequentlyvery desirable separation or sorting of the fibers according to size andweight. More particularly, the coarser and heavier fibers will be thrownfarther away from the entrance opening 15, while the finer and lighterfibers will be sucked down the shortest way towards the wire 1, i.e., bedeposited on the wire closer to the wall member 10. This effect can, ifdesired, be utilized for achieving a certain Stratification ofdifferently sized fibers in the fiber web. Thus, if the wire 1 is drivenas illustrated in FIG. 1 from the left to the right, the lighter andfiner fibers will collect at the bottom of the fiber web, closest to thewire, while the heavier and coarser fibers will be deposited on top ofthe lighter ones. However, by reversing the running direction of thewire 1 approximately the opposite result may be achieved. On the otherhand, the stratification effect may to a certain degree be controlled bymore or less disturbing the flow of gas inside the distribution chamber6 which is also effected by means of the gas streams entering throughthe opening 12. If a very marked disturbance of this kind is desirable,additional gas-admitting, slot-shaped openings may be provided in thehood 11, preferably above the opening 12. It is also possible to changethe position of the opening 12 in the hood in order to vary thedistribution pattern of the fibers.

As should be apparent from the foregoing description the inventionoffers surprising possibilities for the control and variation of theoperation of the apparatus, whereby the advantages of the basicoperating principle may be fully utilized. The apparatus itself isnevertheless relatively simple from a structural point of view and,before all, it is reliable in operation and capable of producing fiberwebs of a high quality and of a great accuracy in thickness at a highspeed from most types of fibers which at all lend themselves totransportation by means of gas streams.

I claim:

1. In the known apparatus for producing a web of dry fibers andcomprising a suction box structure having a substantially rectangulartop opening, a movable beltlike and gas-permeable screen extending oversaid top opening of the suction box structure, a hood-like coverextending over said top opening of the suction box structure and abovethe screen to form a fiber distribution chamber in which said screenforms a substantially horizontal bottom, said distribution chamberhaving a fiber inlet opening vertically spaced from said movable screen,means for moving said screen longitudinally over said top opening of thesuction box structure, a vertical shaft communicating at its upper endwith said fiber inlet opening of the distribution chamber, means forcreating a flow of gas upwardly through said vertical shaft, into saiddistribution chamber, downwardly through said screen and out throughsaid suction box structure, means for suspending fibers in the gasstream rising through said vertical shaft, the improvement whichcomprises:

said vertical shaft being generally rectangular in horizontal crosssection and extending across the full width of said distribution chamberand being separated from said distribution chamber by a substantiallyupright partition wall member extending transversely of the runningdirection of said screen, said partition wall member forming the rearwall of the distribution chamber, said distribution chamber having asection extending in the running direction of said screen that resemblesa sector of a circle, of which one bounding radius is represented bysaid screen, the other bounding radius is represented by said partitionwall member and the arc is represented by curved wall member formingpart of said hood-like cover, said curved wall member being extendedbeyond the upper edge of said partition wall member to form asubstantially horizontal top cover for said vertical shaft and beingvertically spaced from said partition wall member so as to define withthe latter and above the same an opening extending in a vertical planeand representing said fiber inlet opening of the distribution chamber, aslot-like gas inlet opening being provided at the upper end of saidvertical shaft and horizontally opposite to said fiber inlet opening forthe introduction of a second stream of gas in a substantially horizontaldirection across the upper portion of said vertical shaft andimmediately beneath said horizontal top cover thereof and into saiddistribution chamber.

2. An apparatus according to claim 1, wherein said slotlike gas inletopening for the introduction of the second gas stream is variable as toits size.

3. An apparatus according to claim 2, wherein said slotlike gas inletopening is variable as to its configuration.

4. In the known apparatus for producing a web of dry fibers andcomprising a suction box structure having a substantially rectangulartop opening, a movable beltlike and gas-permeable screen extending oversaid top opening of the suction box structure, a hood-like coverextending over said top opening of the suction box structure and abovethe screen to form a fiber distribution chamber in which said screenforms a substantially horizontal bottom, said distribution chamberhaving a fiber inlet opening vertically spaced from said movable screen,means for moving said screen longitudinally over said top opening of thebox structure, a vertical shaft communicating at its upper end with saidfiber inlet opening of the distribution chamber, means for creating aflow of gas upwardly through said vertical shaft, into said distributionchamber, downwardly through said screen and out through said suction boxstructure, means for suspending fibers in the gas stream rising throughsaid vertical shaft, the improvement which comprises:

said vertical shaft being generally rectangular in horizontal crosssection and extending across the full width of said distribution chamberand being separated from said distribution chamber by a substantiallyupright partition wall member extending transversely of the runningdirection of said screen, said partition wall member forming the rearwall of the distribution chamber, said distribution chamber having asection extending in the running directionn of said screen thatresembles a sector ofa circle, of which one bounding radius isrepresented by said screen, the other bounding radius is represented bysaid partition wall member and the arc is represented by a curved wallmember forming part of said hood-like cover, said curved wall memberbeing extended beyond the upper edge of said partition wall member toform a substantially horizontal top cover for said vertical shaft andbeing vertically spaced from said partition wall member so as to definewith the latter and above the same an opening extending in a verticalplane and representing said fiber inlet opening of the distributionchamber, an adjustable slot-like gas inlet opening being provided at theupper end of said vertical shaft and horizontally opposite to said fiberinlet opening for the introduction of a second stream of gas in asubstantially horizontal direction across the upper portion of saidvertical shaft and immediately beneath said horizontal top cover thereofand into said distribution chamber, said arc-forming, curved wall memberhaving at least one inlet opening located approximately midway betweenthe ends of the are formed thereby, said at least one gas inlet openingbeing provided for the introduction of an additional stream of gas in amainly downward direction through said distribution chamber towards saidmovable screen.

5. An apparatus according to claim 4 wherein each of said at least onegas inlet opening of the distribution chamber is variable as to itssize.

6. An apparatus according to claim 4 wherein each of said at least onegas inlet opening of the distribution chamber is adjustable as to itsposition.

7. An apparatus according to claim 4 wherein each of said at least onegas inlet opening of the distribution chamber is variable as to itsconfiguration.

8. An apparatus according to claim 7 wherein individually adjustabledamper means are provided adjacent each of said at least one gas inletopening of the distribution chamber to vary the size and configurationthereof.

9. An apparatus according to claim 8 wherein means for sensing thethickness of the fiber web formed on said movable screen are provided atpoints distributed transversely of said screen and actuating means areprovided for adjusting the setting of said damper means in accordancewith the input to said thickness sensing means.

10. An apparatus according to claim 4 wherein the running direction ofsaid movable screen is reversible.

11. An apparatus according to claim 4 wherein said distribution chamberis provided with a roller that is movable towards and away from saidscreen and adapted to ride on said fiber web, and a hinged flapconnected in sealing engagement with a transverse wall member of saiddistribution chamber rests on said roller.

12. An apparatus according to claim 4 wherein said open box under saidmovable screen is a suction box and said means for creating a flow ofgas is a suction source connected to said box.

13. An apparatus according to claim 4 wherein said means for suspendingfibers in the gas stream rising through said shaft comprises a rotarydisintegrator for breaking up collections of tangled fibers and forthrowing the freed fiber into said vertical shaft and wherein the lowerend of said vertical shaft is connected to a chamber, at the bottom ofwhich conveyor means are provided for removing residues of fibermaterial which the rising stream of gas in said shaft is unable to carryupwardly into said distribution chamber.

1. In the known apparatus for producing a web of dry fibers andcomprising a suction box structure having a substantially rectangulartop opening, a movable belt-like and gas-permeable screen extending oversaid top opening of the suction box structure, a hood-like coverextending over said top opening of the suction box structure and abovethe screen to form a fiber distribution chamber in which said screenforms a substantially horizontal bottom, said distribution chamberhaving a fiber inlet opening vertically spaced from said movable screen,means for moving said screen longitudinally over said top opening of thesuction box structure, a vertical shaft communicating at its upper endwith said fiber inlet opening of the distribution chamber, means forcreating a flow of gas upwardly through said vertical shaft, into saiddistribution chamber, downwardly through said screen and out throughsaid suction box structure, means for suspending fibers in the gasstream rising through said vertical shaft, the improvement whichcomprises: said vertical shaft being generally rectangular in horizontalcross section and extending across the full width of said distributionchamber and being separated from said distribution chamber by asubstantially upright partition wall member extending transversely ofthe running direction of said screen, said partition wall member formingthe rear wall of the distribution chamber, said distribution chamberhaving a section extending in the running direction of said screen thatresembles a sector of a circle, of which one bounding radius isrepresented by said screen, the other bounding radius is represented bysaid partition wall member and the arc is represented by a curved wallmember forming part of said hoodlike cover, said curved wall memberbeing extended beyond the upper edge of said partition wall member toform a substantially horizontal top cover for said vertical shaft andbeing vertically spaced from said partition wall member so as to definewith the latter and above the same an opening extending in a verticalplane and representing said fiber inlet opening of the distributionchamber, a slot-like gas inlet opening being provided at the upper endof said vertical shaft and horizontally opposite to said fiber inletopening for the introduction of a second stream of gas in asubstantially horizontal direction across the upper portion of saidvertical shaft and immediately beneath said horizontal top cover thereofand into said distribution chamber.
 2. An apparatus according to claim1, wherein said slotlike gas inlet opening for the introduction of thesecond gas stream is variable as to its size.
 3. An apparatus accordingto claim 2, wherein said slotlike gas inlet opening is variable as toits configuration.
 4. In the known apparatus for producing a web of dryfibers and comprising a suction box structure having a substantiallyrectangular top opening, a movable belt-like and gas-permeable screenextending over said top opening of the suction box structure, ahood-like cover extending over said top opening of the suction boxstructure and above the screen to form a fiber distribution chamber inwhich said screen forms a substantially horizontal bottom, saiddistribution chamber having a fiber inlet opening vertically spaced fromsaid movable screen, means for moving said screen longitudinally oversaid top opening of the box structure, a vertical shaft communicating atits upper end with said fiber inlet opening of the distribution chamber,means for creating a flow of gas upwardly through said vertical shaft,into said distribution chamber, downwardly through said screen and outthrough said suction box structure, means for suspending fibers in thegas stream rising through said vertical shaft, the improvement whichcomprises: said vertical shaft being generally rectAngular in horizontalcross section and extending across the full width of said distributionchamber and being separated from said distribution chamber by asubstantially upright partition wall member extending transversely ofthe running direction of said screen, said partition wall member formingthe rear wall of the distribution chamber, said distribution chamberhaving a section extending in the running direction of said screen thatresembles a sector of a circle, of which one bounding radius isrepresented by said screen, the other bounding radius is represented bysaid partition wall member and the arc is represented by a curved wallmember forming part of said hood-like cover, said curved wall memberbeing extended beyond the upper edge of said partition wall member toform a substantially horizontal top cover for said vertical shaft andbeing vertically spaced from said partition wall member so as to definewith the latter and above the same an opening extending in a verticalplane and representing said fiber inlet opening of the distributionchamber, an adjustable slot-like gas inlet opening being provided at theupper end of said vertical shaft and horizontally opposite to said fiberinlet opening for the introduction of a second stream of gas in asubstantially horizontal direction across the upper portion of saidvertical shaft and immediately beneath said horizontal top cover thereofand into said distribution chamber, said arc-forming, curved wall memberhaving at least one inlet opening located approximately midway betweenthe ends of the arc formed thereby, said at least one gas inlet openingbeing provided for the introduction of an additional stream of gas in amainly downward direction through said distribution chamber towards saidmovable screen.
 5. An apparatus according to claim 4 wherein each ofsaid at least one gas inlet opening of the distribution chamber isvariable as to its size.
 6. An apparatus according to claim 4 whereineach of said at least one gas inlet opening of the distribution chamberis adjustable as to its position.
 7. An apparatus according to claim 4wherein each of said at least one gas inlet opening of the distributionchamber is variable as to its configuration.
 8. An apparatus accordingto claim 7 wherein individually adjustable damper means are providedadjacent each of said at least one gas inlet opening of the distributionchamber to vary the size and configuration thereof.
 9. An apparatusaccording to claim 8 wherein means for sensing the thickness of thefiber web formed on said movable screen are provided at pointsdistributed transversely of said screen and actuating means are providedfor adjusting the setting of said damper means in accordance with theinput to said thickness sensing means.
 10. An apparatus according toclaim 4 wherein the running direction of said movable screen isreversible.
 11. An apparatus according to claim 4 wherein saiddistribution chamber is provided with a roller that is movable towardsand away from said screen and adapted to ride on said fiber web, and ahinged flap connected in sealing engagement with a transverse wallmember of said distribution chamber rests on said roller.
 12. Anapparatus according to claim 4 wherein said open box under said movablescreen is a suction box and said means for creating a flow of gas is asuction source connected to said box.
 13. An apparatus according toclaim 4 wherein said means for suspending fibers in the gas streamrising through said shaft comprises a rotary disintegrator for breakingup collections of tangled fibers and for throwing the freed fiber intosaid vertical shaft and wherein the lower end of said vertical shaft isconnected to a chamber, at the bottom of which conveyor means areprovided for removing residues of fiber material which the rising streamof gas in said shaft is unable to carry upwardly into said distributionchamber.